Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2001
Publication Date: N/A
Interpretive Summary: The wheat stem sawfly is a major pest limiting the production of wheat in the Northern Great Plains of North America. Insecticides are ineffective against the damaging larvae eating inside the wheat stem, and adult emergences in the field are difficult to predict. Understanding the behavior and the chemical communication of the wheat stem sawfly could lead to new and environmentally friendly approaches for reducing agricultural damage. Using field and laboratory studies, we were able to describe the intricate behaviors and interactions of the insects prior to mating. The behaviors and interactions were triggered by the release of chemical signals (pheromones), which enabled the insects to aggregate in wheat fields. Synthetic versions of two of the chemicals present in the pheromone blend were tested in a wheat field and in the laboratory, and the data demonstrated that the release of these synthetic compounds can trigger the observed insect behaviors and interactions prior to mating. This study has defined the insects' behaviors and interactions that are important in the chemical communication of wheat stem sawfly, and this information supports the design of an environmentally friendly method of controlling this agricultural pest.
Technical Abstract: Pre-mating behavior of the wheat stem sawfly, Cephus cinctus (Norton), was observed in the field and was studied in the laboratory. Mating in the field was observed only during sunny, warm, relatively calm weather. Certain behaviors consistently preceded mating: In both sexes, these included raising of the abdomen and rubbing with hind legs, antennal tapping, antennal grooming, and wing fanning. These behaviors were accompanied by short flights, particularly by males, which often ended by landing near females and quickly mating. Groups of males frequently engaged in the flight behavior at the same time, in the manner of leks. In a static-air olfactometer in the laboratory, the abdominal raise-and-rub behavior occurred significantly more often with pairs that subsequently mated than with pairs that did not. In a moving-air, Y-tube olfactometer, both virgin males and virgin females were more attracted to other virgin sawflies of either sex than to a control air stream. However, females were not attracted to individual males but only to grouped males, which correlates to an earlier observation that grouped males, but not individual males, emit phenylacetic acid. The interactions among groups of sawflies were observed in a brightly lit wind tunnel containing potted wheat plants and were similar to those observed in the field. Finally, one previously identified, antennally active compound derived from both sexes, 9-acetyloxynonanal, was shown to be significantly attractive in the field when the synthetic compound was used to bait traps.